This competing renewal application requests continuation of a clinical research center engaged in the clinical study of multichannel cochlear implants. The overall goal of the research is to improve the performance of deafened adults and children using cochlear implants. Field trials of different multichannel cochlear implants have resulted in a wide range of performance outcomes among individuals using the same type of implant. The continuous interleaved sampling speech coding algorithm appears to represent the best available speech coding strategy. However, the number of fitting parameters is large. It is hypothesized that outcome can be significantly enhanced by more systematic adjustment of speech processor fitting algorithms. The proposed application will test this hypothesis in 121 postlingually deafened adults and prelingually deafened children previously implanted with multichannel cochlear implants at our center and 70 newly-recruited profoundly deafened adults and children who will be implanted with a new state-of-the-art cochlear implant (CI-24M). The CI- 24M has been designed to precisely monitor residual intracochlear auditory function in different regions of the cochlea and to perform electrophysiologic measures developed by members of the Iowa Cochlear Implant Center. Electrophysiologic and psychophysical measures will be used to define speech coding fitting algorithms to be field tested in clinical trials using this large population. Five research projects, an Administrative Core A and a Patient Care and Technical Support Core B will address the following aims: 1) determine whether individual variables, such as precise intracochlear localization of residual auditory nerve function, can be used to define speech processor fitting parameters; 2) conduct field trials using different speech processor programs to determine the effectiveness of these speech coding strategies on populations that display a wide range of performance; 3) better understand the subject characteristics (ie: physiologic, cognitive, behavioral, and environmental) that influence and are predictive of outcome with a cochlear implant to develop models that can be used select the most appropriate hearing rehabilitation strategy for an individual; 4) continue longitudinal studies aimed at understanding the effect that age at implantation has on development of speech perception, speech production, language, and sign in a population of prelingually deafened children; 5) determine if a structured listening protocol with a broad range of musical stimuli can enhance user satisfaction and consequently quality of life; 6) determine preoperatively which ear should receive a cochlear implant; and 7) measure the binaural effects of cochlear implants.